The invention relates to an at least substantially metallic flat gasket with a gasket plate comprising at least one sheet metal layer, at least one fluid through-opening to be sealed (in the case of a cylinder head gasket, for example, for the passage of combustion gases or cooling water or lubricating oil), and a plurality of screw through-openings for the passage of screws therethrough for clamping the flat gasket between sealing surfaces of components (for example, the sealing surfaces of a cylinder head and an engine block), the sheet metal layer having at least one supporting element for receiving pressing forces acting on the flat gasket when the flat gasket is installed, and the supporting element comprising at least one bead stamped into the sheet metal layer and having a bead crest forming a continuous line.
The invention will be explained hereinbelow with reference to cylinder head gaskets, although a flat gasket according to the invention is also suitable for other applications, for example, for a gasket between a cylinder head and an exhaust manifold, or for a so-called flange gasket between flanges of two pipes or other components to be joined to one another by screws.
In single-layered and multi-layered metallic cylinder head gaskets, sealing around the combustion chamber through-openings of the gasket plate is usually effected by sealing beads stamped into one sheet metal layer or several sheet metal layers. These sealing beads enclose the combustion chamber through-openings and are mostly formed as so-called full beads with a circular arc-shaped or approximately U-shaped cross section. As these sealing beads must have elastic properties in the direction of their height, so as to also fulfill their sealing function during operation of the engine, a sheet metal layer provided with sealing beads is made of spring steel. In order to prevent the sealing beads from becoming excessively flattened when the cylinder head gasket is being installed and during operation of the engine and thereby becoming damaged (as a result of permanent breakages), the sealing beads have associated deformation delimiters (so-called stoppers), which are thickened zones of one or several sheet metal layers. When the cylinder head gasket is installed and the engine is in operation, these stoppers receive some of the pressing forces acting on the cylinder head gasket after the sealing beads have been flattened somewhat elastically owing to these pressing forces. Accordingly, these stoppers are not only deformation delimiters but also supporting elements which are associated with the sealing beads enclosing the combustion chamber through-openings. However, the present invention does not relate to such supporting elements as are associated with combustion chamber sealing beads and enclose combustion chamber through-openings.
Above all, in single-layered and multi-layered metallic cylinder head gaskets, thickened supporting elements are also used at other places than around cylinder head gasket openings to be sealed, and the present invention relates to such supporting elements. In a multi-cylinder engine, the usual position of the cylinder head screws results in the cylinder head being drawn in the area of its narrow sides, i.e., its longitudinal ends, with a stronger tendency downwards, i.e., in the direction towards the engine block, than in other areas of the cylinder head. Moreover, when the engine is in operation, the high gas pressures prevailing in the combustion chambers cause the cylinder head to arch up between its longitudinal ends (albeit slightly) during operation of the engine. These two effects have already been counteracted by providing the cylinder head gasket in the area of its longitudinal ends with thickened zones which serve as elevated supporting elements for the longitudinal ends of the cylinder head. However, since a multi-cylinder reciprocating piston engine is often more susceptible to deformation in the areas of its longitudinal sides, for example, on account of the inlet and outlet ports, than in other areas, elevated supporting elements have also already been provided at the longitudinal sides of the cylinder head gaskets.
U.S. Pat. No. 5,427,389-A discloses a multi-layered metallic cylinder head gasket of the kind mentioned at the outset, wherein a sheet metal layer lying inside the approximately rectangular gasket plate is provided in the end areas of this sheet metal layer in the vicinity of the two narrow sides of the gasket plate with supporting elements which are full beads stamped into this sheet metal layer. The following three different embodiments are disclosed for these supporting beads: in the first embodiment, each of the two aforementioned end areas of the sheet metal layer is provided with a straight-lined supporting bead extending in the proximity of the respective narrow side edge of this sheet metal layer and parallel thereto; in the second embodiment, the supporting bead has approximately the shape of a lying U and extends parallel to the adjacent narrow side edge and over a certain distance parallel to the two longitudinal side edges of the sheet metal layer; in the third embodiment, the supporting bead is, in a plan view of the sheet metal layer, of wave-like configuration and extends in the vicinity of the pertinent narrow side edge of the sheet metal layer approximately parallel to this narrow side edge. As has been ascertained by the firm of ElringKlinger AG, all of these supporting beads have the disadvantage that, when the engine is in operation, they exhibit wear phenomena, starting off from the free bead ends, which increase as the operating time increases, and the cause of which has not been able to be fully clarified. It is also to be assumed that the same or similar wear phenomena occur with other flat gaskets of the kind mentioned at the outset whenever the flat gasket is subjected to dynamic stresses, in particular, load variations, when in operation.
The object underlying the invention was to create a flat gasket of the kind mentioned at the outset, in which the at least one supporting element formed by at least one bead has a longer service life in operation, i.e., is subject either to no wear or to only a significantly lower degree of wear than the supporting beads disclosed by U.S. Pat. No. 5,427,389-A.